第三代同步輻射的發展對奈米材料電子結構的探討提供了強而有力的能譜技術，包括X光吸收能譜術(XAS)(主要是X光吸收近緣結構能譜，XANES)、X光光電子能譜術(XPS)、掃描式光電子顯微能譜術(SPEM)、X光磁圓偏振二向性(XMCD)和X光輻射能譜術(XES)已然被廣泛應用在了解奈米碳管(CNTs)、氧化鋅(ZnO)和氧化鈷鋅奈米柱(Zn1-xCoxO nanorods)、氮化鎵奈米線(GaN nanowires)及氮化鋁奈米針(AlN nanotips)等奈米材料電子結構的佔據態和未佔據態。
藉由不同入射角度的量測，我們可以比較奈米碳管和氧化鋅奈米柱在尖端和側面的局域電子結構。從結果發現，奈米碳管的尖端具有相當均勻且延伸了大約10 eV的價帶強度;而在氧化鋅方面則發現，奈米柱的尖端主要是由氧原子所佔據，並且沿著[000 ]方向成長。針對不同管徑氧化鋅奈米柱量測鋅和氧的K邊X光吸收近緣結構能譜圖，得知管徑愈小則所受的表面效應愈大。
在氧化鋅奈米柱的成長過程中添加鈷元素使其成為帶有鐵磁性的稀磁性半導體的能譜研究中，提出了鐵磁性的產生和深層缺陷的電子轉移至價帶的鈷3d軌道有很強烈的關聯性。比較氮化鎵奈米線和氮化鎵薄膜，因為負(正)電荷效應的增加所以造成奈米線中氮(鎵) 的K邊X光近緣結構能譜圖具有較大(小)的強度。除此外，在p-type和n-type矽基板上成長氮化鋁奈米針的SPEM研究中可以看到，在靠近費米面的地方，AlN/p-Si擁有較大的態密度。

The development of third generation synchrotron radiation sources has provided powerful spectroscopic techniques for probing the electronic structures of nanomaterials. Primarily five techniques namely; X-ray absorption spectroscopy (XAS) (mainly X-ray absorption near edge structure, XANES), X-ray photoelectron spectroscopy (XPS), scanning photoelectron microscopy (SPEM), X-ray magnetic circular dichroism (XMCD), and X-ray emission spectroscopy (XES), have been extensively employed to understand the unoccupied as well as occupied states of electronic structures of nanomaterials; carbon nanotubes (CNTs), ZnO & Zn1-xCoxO nanorods, GaN nanowires, and AlN nanotips. 
Angle-dependent measurements were performed to understand the local electronic structures of the tips and sidewalls of highly aligned CNTs and ZnO nanorods. It suggests that increase in tip intensities is quite uniform over an energy range wider than 10 eV and the tip surfaces of the highly aligned ZnO nanorods are terminated by O atoms and the nanorods are oriented in [000 ]. An analysis of XANES spectra at O K- and Zn K-edge of ZnO nanorods at various diameters showed enhancement of surface states with decrease of diameter. Spectroscopic studies on Zn1-xCoxO nanorods showed that the ferromagnetism is strongly associated with the transfer of electrons from deep defect states to valence-band Co 3d orbitals. A comparison of the XANES spectra at N (Ga) K-edge revealed that the GaN nanowires have smaller (larger) intensity than that of GaN thin film, which suggests an increase of the N (Ga) negative (positive) effective charge in the nanowires. Apart from this, a comparison of the electronic structures was carried on AlN nanotips grown on p- and n-type Si substrates and the SPEM study indicates that the former have larger density of states than the latter near Fermi level.

Table of Contents
Abstract ……………………………………………………………iii

List of Figures ……………………………………………………vii

1.	Introduction
1-1.	Nanoscience and Nanotechnology. ……………………………………1
1-2.	Need for Spectroscopic Studies. ………………………………………2

2.	Experimental Techniques
2-1.	Synchrotron Radiation. ………………………………………………6
2-2.	X-ray Absorption Spectroscopy (XAS). …………………………9
2-3.	X-ray Photoemission Spectroscopy (XPS). …………………………22
2-4.	Scanning Photoelectron Microscopy (SPEM). ………………………24
2-5.	X-ray Magnetic Circular Dichroism (XMCD). ……………………27
2-6.	X-ray Emission Spectroscopy (XES). ………………………………31

3.	Electronic Structure of Carbon Nanotubes
3-1.	Introduction. ……………………………………………………………33
3-2.	Experimental. …………………………………………………………34
3-3.	Results and Discussion. ………………………………………………35
3-4.	Conclusion. ……………………………………………………………42

4.	Electronic Structure of ZnO Nanorods
4-1.	Angle-dependent of ZnO Nanorods. ……………………………43
4-1.1.	Introduction. ………………………………………………………43
4-1.2.	Experimental. ……………………………………………………44
4-1.3.	Results and Discussion. …………………………………………46
4-1.4.	Conclusion. ………………………………………………………53
4-2.	Diameter-dependent of ZnO Nanorods. …………………………54
4-2.1.	Introduction. ………………………………………………………54
4-2.2.	Experimental. ……………………………………………………54
4-2.3.	Results and Discussion. …………………………………………57
4-2.4.	Conclusion. ………………………………………………………65


5.	Electronic and Ferromagnetic Properties of Zn1-xCoxO Nanorods
5-1.	Introduction. ……………………………………………………………66
5-2.	Experimental. …………………………………………………………67
5-3.	Results and Discussion. ………………………………………………69
5-4.	Conclusion. ……………………………………………………………79

6.	Electronic Structure of GaN Nanowires and AlN Nanotips
6-1.	The Study of GaN Nanowires. ………………………………………80
6-1.1.	Introduction. ………………………………………………………80
6-1.2.	Experimental. ……………………………………………………81
6-1.3.	Results and Discussion. …………………………………………83
6-1.4.	Conclusion. ………………………………………………………90
6-2.	The Study of AlN Nanotips. …………………………………………91
6-2.1.	Introduction. ………………………………………………………91
6-2.2.	Experimental. ……………………………………………………92
6-2.3.	Results and Discussion. …………………………………………93
6-2.4.	Conclusion. ……………………………………………………102


7.	Summary. ………………………………………………………………103


Bibliography. ………………………………………………………………106


List of Figures
2-1.	The schematic when synchrotron radiation strikes matter. ………………8
2-2.	The photoelectron scattering process in the (a) multiple scattering regime, XANES and (b) single scattering regime, EXAFS. ………………………9
2-3.	A typical x-ray absorption spectrum showing XANES and EXAFS regions. …………………………………………………………………10
2-4.	The schematic of various methods of measurements. ……………………15
2-5.	A commonly used procedure for background removal for either transmission absorption data μ(E) vs. E. The pre-edge fit (dash-dot curves) is then subtracted from the total absorption data to give the “elemental absorption” μ(E) vs. E shown as the solid curve, the edge-jump μE and the experimental energy threshold E ′ can be determined. …………………18
2-6. Data reduction and analysis in EXAFS spectroscopy: (a) EXAFS spectrum
χ(k) vs. k after background removal, normalization, and E to k conversion;
(b) the solid curve is the weighted EXAFS spectrum k3χ(k) vs. k. The
dashed curve is the fit. ……………………………………………………19
2-7. Data reduction and analysis in EXAFS spectroscopy: (a) FT of the
weighted EXAFS spectrum in momentum (k) space into distance (r) space.
The dashed curve is the window function; (b) Fourier-fitted EXAFS
spectrum (solid curve) of the major peak in (a) after back transformed into
k space and fit the filtered data shown in dashed curve. …………………21
2-8. XPS as a three-step process: (a) photoexcitation of electrons; (b) travel to
the surface with concomitant production of secondaries (shaded); (c)
penetration through the surface (barrier) and escape into the vacuum. Φ is
the work function; VB E Δ is the difference between valence level and
Fermi level. ………………………………………………………………23
2-9. Schematic diagram of the U5-SPEM system. ……………………………26
2-10. Electronic transitions in conventional L3,2-edge x-ray absorption (a), and
XMCD (b,c), illustrated in a one-electron model. The transitions occur
from the spin-orbit split 2p core shell to empty conduction band states. In
conventional x-ray absorption the total transition intensity of the two peaks
is proportional to the number of d holes. By use of circularly polarized
x-rays the spin moment (b) and orbital moment (c) can be determined from
linear combinations of the dichroic difference intensities A and B,
according to other sum rules. ……………………………………………29
2-11. The schematic representation of (a) XPS (b) XAS, and (c) XES. ………32
2-12. The relation of XPS, XAS, and XES. ……………………………………32
3-1. (a) SEM image and (b) TEM image of the well-aligned multiwalled CNTs
with diameters of 10~20 nm. ……………………………………………35
3-2. Normalized C K-edge absorption spectra of the aligned CNTs as a function
of θ. The inset shows an enlarged part of the near-edge spectra. ………37
3-3. Cross-sectional SPEM image of aligned CNTs. …………………………38
3-4. (a) Valence-band spectra and (b) C 1s photoemission spectra from the three
selected regions marked by A, B, and C shown in Fig. 3-3, which
correspond to tip, bright area, and dark area, respectively. ……………40
4-1. (a) SEM image and (b) HRTEM image and its corresponding electron
diffraction (inset) of the ZnO nanorods. ……………………………45
4-2. The O K-edge XANES spectra of ZnO nanorods for various photon
incident angles. The inset defines the photon incident angle. ……………48
4-3. The Zn K-edge XANES spectra of ZnO nanorods for various photon
incident angles. The inset plots the Zn L3-edge XANES spectra. ………49
4-4. Valence-band SPEM spectra obtained from regions marked by t1-t3 and
s1-s3 shown in the upper inset, which displays SPEM Zn 3d cross-sectional
image of ZnO nanorods. The lower inset shows the Zn 3d core-level
photoemission spectra from regions t1-t3 and s1-s3, respectively. ………51
4-5. XRD measurements of the well-aligned ZnO nanorods with 45 nm, 80 nm
and 150 nm diameters and the reference thin film. The insets (a) and (b)
ix
show representative SEM and TEM images of the 45 nm nanorod,
respectively. ………………………………………………………………56
4-6. O K-edge XANES spectra of the well-aligned ZnO nanorods with 45 nm,
80 nm, and 150 nm diameters and the reference film. The upper and lower
insets show the magnified main features after background subtraction and
the edge features, respectively. …………………………………………58
4-7. Zn L3-edge XANES spectra of the ZnO nanorods with 45 nm, 80 nm, and
150 nm diameters and the reference film. The upper inset shows the
magnified main near-edge features after background subtraction. The lower
inset shows the integrated intensities of O K- (open circles) and Zn
L3-edges (filled circles) near-edge features. ……………………………60
4-8. Zn K-edge XANES spectra of the ZnO nanorods with 45 nm, 80 nm, and
150 nm diameters and the reference film. The inset shows the magnified
feature B3. ………………………………………………………………62
4-9. Valence-band photoemission spectra obtained from selected positions p, q,
r, and s shown in the upper inset, which shows the Zn 3d SPEM
cross-sectional images of the well-aligned ZnO nanorods with 45 nm, 80
nm and 150 nm diameters and the top view of the reference film,
respectively. The lower inset presents the Zn 3d core-level spectra from
positions p, q, r, and s. …………………………………………………64
5-1. (a)The insets show representative SEM and (b) TEM images and the
corresponding electron diffraction from Zn1-xCoxO (x= 0.057)
nanorods. …………………………………………………………………68
5-2. (a) XRD measurements of well-aligned Zn1-xCoxO and ZnO nanorods and
the reference CoO powder and Co metal (the intensity in log unit.). (b)
presents the Fourier transform amplitudes of the EXAFS k3χ data at the Co
and Zn K-edge from 3.2 to 13 Å for Zn1-xCoxO, ZnO nanorods, CoO
powder and the Co metal, respectively. …………………………………70
5-3. Normalized Co L3,2-edge XANES and XMCD spectra of Zn1-xCoxO
nanorods and the reference Co metal. ……………………………………72
5-4. Magnified view of XMCD features of Zn1-xCoxO nanorods and thereference Co metal at the Co L3-edge. The upper inset presents the
integrated intensities of the negative prominent features in the Co L3-edge
XMCD spectra as functions of the Co content. The lower inset plots
hysteresis loops of Zn1-xCoxO nanorods with x= 0.057 and 0.061 at room
temperature. ………………………………………………………………73
5-5. Co L3,2-edge XANES spectra of Zn1-xCoxO and ZnO nanorods and the
reference CoO powder and Co metal. The inset shows the O K-edge
XANES spectra of the Zn1-xCoxO and ZnO nanorods. …………………75
5-6. Valence-band photoemission spectra obtained from selected positions p, q,
and r in Zn 3d SPEM cross-sectional images of well-aligned x=0.061 and
0.057 Zn1-xCoxO and ZnO nanorods. The lower inset plots difference
valence-band spectra between Zn1-xCoxO and ZnO nanorods. …………77
6-1. (a) SEM image and (b) HRTEM image and its corresponding electron
diffraction (inset) of GaN nanowires. ……………………………82
6-2. (a) Normalized N K- and (b) Ga K-edge XANES spectra of GaN nanowires
and thin film. ……………………………………………………………84
6-3. Normalized Ga L3-edge XANES spectra of GaN nanowires and thin
film. ………………………………………………………………………86
6-4. (a) Valence-band and (b) Ga 3d core-level SPEM spectra from the regions
marked by A-E shown in the insets, which present the SPEM Ga 3d images
of a bunch of nanowires (upper inset) and thin film (lower inset). ………88
6-5. XRD measurements of quasi-aligned AlN nanotips and the reference thin
film. The insets (a)-(c) display representative SEM images of the top-view
of p- and n-type AlN nanotips and the cross-sectional view of p-type AlN
nanotips, respectively. The inset (d) plots field-emission characteristic
curves of p- and n-type AlN nanotips. …………………………………94
6-6. Al and N (lower inset) K-edge XANES spectra of AlN nanotips and the
reference thin film. The upper inset shows the incident angle θ relative to
the c-axis of nanotips. ……………………………………………………96
6-7. Valence-band photoemission spectra summed over selected positions
p(s1)-p(s3), n(s1)-n(s3) and f(1)-f(3) shown in the upper inset, which
xi
present the Al 2p SPEM cross-sectional images of quasi-aligned AlN
nanotips and the top view of the reference thin film, respectively. The
lower inset presents the valence-band photoemission spectra summed over
the selected tip regions p(t1)-p(t3) and n(t1)-n(t3), shown in the upper
inset. ……………………………………………………………………98
6-8. Displays XES and corresponding XANES of the N 2p states of AlN
nanotips and the reference thin film. ……………………………………101

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